Lasers and Optics

Dr. Herman Batelaan

DEPARTMENT OF PHYSICS & ASTRONOMY

Double-Slit Experiments

REU students will work in Batelaan’s laboratory on our acoustic double-slit analogue and our quantum dot double-slit experiment. Both experiments are intended for educational demonstrations and outreach. The acoustic double slit uses Schlieren imaging to observe sound waves in real time, while the quantum-dot double slit affects the amount of coherence of the fluorescent light source and thus the visibility of the double-slit diffraction pattern. Our Augmented Reality application for our real electron double slit-experiment is situated in the adjacent lab and helps provide inspiration and visualization goals for the demonstration experiments.

Dr. Martin Centurion

DEPARTMENT OF PHYSICS & ASTRONOMY

Ultrafast Dynamics

The Ultrafast Dynamics group of Centurion investigates the conversion of light into chemical and mechanical energy at the molecular level. Upon absorption of a photon, a molecule undergoes structural transformations on the femtosecond scale, which lead to the breaking and making of chemical bonds, changes in the molecular geometry and its properties. To understand these transformations, it is essential to observe them on their natural spatiotemporal scales of sub-angstroms and femtoseconds. We have developed an instrument to carry out ultrafast electron diffraction experiments on isolated molecules, which proved atomic resolution on the femtosecond scale. With this, we can capture the nuclear motions triggered by light and follow the structural re-arrangements leading to the formation of different molecules. Our work involves femtosecond-pulsed lasers, generation and characterization of femtosecond electron pulses and retrieving structures from electron diffraction patterns. Previous student projects have involved work on sample delivery, characterization of laser and electron pulses, automation of experimental components, and simulation of electron pulse propagation and data analysis.

Dr. Timothy Gay

DEPARTMENT OF PHYSICS & ASTRONOMY

Polarized Electrons

Dr. Gay’s research uses polarized electrons and anti-electrons (positrons) to study spin-dependent effects in scattering from chiral biological molecules. In addition, his group is developing new types of polarized electron sources based on secondary electron emission from GaAs. 

(1) Studies of Polarized Electron Collisions with Chiral Molecules. How does chiral symmetry breaking affect the scattering of polarized electrons or positrons by chiral molecules? The underlying collision dynamics are unknown. Our recent observation of chirality-dependent molecular dissociation has provided an important validation of the Vester-Ulbricht hypothesis, which seeks to explain the origin of biological homochirality. This is one of the most fundamental questions in science. One REU project in this effort would be the characterization of our positron sources that we use for these collision studies in terms of their intensity and helicity.   

(2) Studies of Polarized Secondary Electron Emission from GaAs. The standard source of polarized electrons is CW photoemission from GaAs. The operation of such a source requires very clean, ultra-high vacuum and the placement of atomic layers of cesium and oxygen on the GaAs surface to allow photo-excited electrons to be emitted from the solid into the vacuum. These conditions are technically very difficult to maintain; the Cs-O overlayer can be easily contaminated by residual CO and organic hydrocarbons preventing electron emission altogether. We are working to develop a source that doesn’t have such stringent vacuum requirements. A CW laser would excite electrons in the GaAs into excited states, polarizing them at the same time. A beam of unpolarized electrons would then be used to kick these excited electrons into the vacuum, making a polarized “secondary” electron beam. An REU student working on this project would determine the secondary electron yield of a variety of GaAs samples with varying crystal morphologies and doping concentrations to find an optimal target for our experiments.

Dr. Eva Schubert

DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING

Metamaterials

The Schubert lab has expertise in metamaterial fabrication, characterization, and optical in-situ growth monitoring. The lab employs bottom-up methods for self-organized growth such as oblique angle deposition (OAD) and atomic layer deposition and extensively uses in-situ spectroscopic ellipsometry for real time growth monitoring. Metamaterials are particularly of interest for photonic and optical applications in sensors, filters, polarization-sensitive devices and for light harvesting. Si nanospirals, as a specific metamaterial, have intriguing chiro-optical properties such as tunable circular dichroism and optical activity. Small chiro-optical responses and limits in spectral tunability impose obstacles for applicability in devices. Heterostructure nanospirals from Si-Me (Me…Au or Ag) may offer an alternative route to overcome these limitations by adding a plasmonic element through the metal component.

In the 10-week REU period, the student will (a) learn to prepare chiral metamaterials via oblique angle deposition and characterize their geometry using scanning electron microscopy, and (b) measure and analyze the chiro-optical properties for Si-Me nanospirals by means of Muller-Matrix spectroscopic ellipsometry. Through these studies, the student will receive training in operating ultra-high vacuum systems, and material deposition by e-beam evaporation and ion beam assisted deposition. The student will learn how to operate commercial spectroscopic ellipsometry equipment and will be introduced to optical data analysis using modern regression algorithms.           

Dr. Kees Uiterwaal

DEPARTMENT OF PHYSICS AND ASTRONOMY

Propagation of Optical Vortices

The research group of Uiterwaal studies the propagation of ultrafast pulses of light through liquid media. We do this by detecting fluorescence after two two-photon absorption. This research sheds light on the spatiotemporal qualities (including phases) of the pulse, and on the dispersive properties of the liquid. For propagation under linear optical conditions, we have demonstrated we can analyze up to third-order temporal phases for pulses as short as 8 femtoseconds. We have recently started to explore non-linear propagation. Under non-linear conditions two pulses are expected to interact. In our research we plan to make use of pulsed optical vortices. Our group has experience with creating these using printed computer-generated holograms photographed on slides or laser-etched holographic gratings. In the past, undergraduates have recorded and analyzed beam images and measured two-photon cross sections of the dyes we use in our research. Previous REU students have also built Augmented Reality applications to model non-linear propagation and to improve understanding.

Dr. Chris Varney

DEPARTMENT OF PHYSICS AND ASTRONOMY

Optical Simulations in Augmented Reality

Student lab experiments in optics and electromagnetic waves face challenges ranging from high cost and limited availability of specialized equipment to safety risks of high-power light sources, and the complexity of abstract concepts involved in the experiment. Computer-based training has been shown to improve conceptual understanding and Augmented Reality (AR) is particularly suited for enhancing learning by visualizing complex processes that are otherwise imperceptible. This research project proposes the development of AR simulations designed to serve as a supportive companion for introductory physics optics laboratory experiments. The aim is to leverage AR’s distinctive capabilities to enhance students’ conceptual understanding, engagement, and practical skills in optics.

Dr. Craig Zuhlke

DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING

Femtosecond Laser Surface Processing

The Center for Electro-Optics and Functionalized Surfaces (CEFS) at U. Nebraska- Lincoln has developed techniques to directly functionalize or tailor the surface properties of metals using a technique known as femtosecond laser surface processing (FLSP). With FLSP, the properties of metals are altered by creating self-organized micro- and nano-scale surface structures combined with laser-induced sur-face and subsurface microstructure and chemistry changes using finely controlled ultra-short laser-matter interactions. FLSP can be used to change the wetting properties of surfaces, to make surfaces superhydrophobic or superhydrophilic, or alter the optical properties of a surface (e.g. create broadband absorbing or high emissivity surfaces). FLSP is a transformative technique with several distinct advantages compared to traditional surface functionalization techniques, such as lithography or coatings, because surface features are generated directly on the metallic surface through a combination of preferential laser ablation, fluid flow, plasma driven processes, and redeposition of ablated material in the form of nanoparticles. The FLSP surfaces are highly permanent, scalable, do not suffer from the delamination issues often associated with coatings, and can be finely tuned to specific applications. 

In recent research, CEFS has shown that these femtosecond laser functionalized surfaces are useful in producing superhydrophobic surfaces, enhancing two phase heat transfer, altering optical absorption, producing anti-icing and anti-microbial surfaces, reducing drag, and producing high emissivity surfaces. The wide range of applications of FLSP, state-of-the-art femtosecond laser and materials analysis research facilities, and the large multidisciplinary research program by CEFS provides several opportunities for undergraduate students to be involved in research.